Created 01/15/2003 - Updated 03/09/2010

Wherein, S.W. Williston describes, for the first time, an intact skull of an
American plesiosaur (Styxosaurus snowii, KUVP 1301, currently in the exhibits of
the University of Kansas Museum of Natural History), including the first evidence of a
sclerotic ring. To date, this is the only known skull of an elasmosaur from Kansas.

262
SCIENCE.
[VOL. XVI.
No. 405

Structure of the Plesiosaurian Skull.

IT is somewhat remarkable, that, in a
group of fossil reptiles like the plesiosaurs, the nature and structure of the skull
should have remained for so long a time practically unknown. Fragmentary remains of this
very important part of the skeleton are not rare in collections, but none sufficiently
complete to make out any thing at all satisfactory of its anatomy have hitherto been
described. Very fortunately the museum of the Kansas University has recently been enriched
by the skull and a large part of the neck of one of
these animals, in most remarkably perfect preservation, collected from the Kansas Niobrara cretaceous by Judge E. P. West, assistant in
paleontology at the State University. Recognizing the value and rarity of the specimen,
Dr. West used the most scrupulous care in removing and shipping the specimen, and, as now
cleaned from its matrix in the museum, it permits most of its structure to be made out
with certainty and ease. I have in preparation a full description of the specimen, with
illustrations, which will shortly be published in the "Transactions of the Kansas
Academy of Sciences." Meanwhile, however, the very great importance of the find
renders a brief description of its chief characters at the present time very desirable.
The species I refer provisionally to the genus Cimoliasaurus
[sic], though certain characters, as will be seen, do not accord with those given by
Lydekker in his recent "Catalogue of Fossil Reptilia," The specimen lies upon
its side, with twenty-six vertebrę in position; and all, save some of the posterior
vertebrę, which were exposed, are in perfect preservation. The cervical vertebrę have
the arches and riblets fully co-ossified with no or but very slight traces of their
sutural attachments. There is but a single rib attachment, and the zygosphene is
rudimentary, The spines are short; the anterior centra, gently cupped; the posterior ones,
which increase gradually in slenderness, more deeply so. The parietal bone forms a roof-
shaped covering, ascending into a high, thin sagittal crest two or three inches above the
brain-case: there is no parietal foramen. There is but one temporal arcade, a broad bar
passing directly backward, on a line with the maxilla, to unite with the lower part of the
quadrate, The limits of the quadrato-jugal have not yet been satisfactorily made out. The
post-orbital is a slender bone uniting broadly with the jugal below, and has no connection
with the slender squamosal. There is apparently no post-frontal. Lying within the
comparatively small orbit are eleven or twelve sclerotic plates, touching each other at
their edges, and forming the larger part of a ring, a few having been misplaced. The
mandibular symphysis is short, and the two sides' are so firmly co-ossified that I have
found no trace of the suture. There are about twenty teeth in each jaw, extending far
back, the anterior ones very much larger than the posterior ones; in the locked jaws the
upper ones reaching nearly to the lower margin of the stout mandible. A part of a single
bone was found between the jaws, which I believe to pertain to a hyoid.

I need not point out the importance of the foregoing
characters. Others scarcely less interesting will he given later. The ones here given,
however, are nearly all in conflict with generic, family, ordinal, or even super-ordinal
characters hitherto accepted, The sclerotic plates are the first ones described for any of
the Synaptosauria, a branch comprising the Chelonia and Sauropterygia.

The species can be located with neither Polycotylus
or Elasmosaurus, the two genera of the American
cretaceous hitherto described as having co-ossified neural arches. I place it, however,
under Cimoliasaurus [sic], in Lydekker's acceptation, and shall describe and
figure it under the name C. Snowii, in honor of Chancellor
F. H. Snow, who has done so much for the development of the natural-history department
of our university, I append a few measurements: length of skull from occipital condyle to
top of premaxilla, 18 inches; greatest height of skull to top of parietal crest, 9 inches;
length of centrum of second cervical vertebra, 1 3/8 inches; height
of centrum of second cervical vertebra, 1 3/8 inches; height of
spine above centrum. same vertebra, 2½ inches; length of centrum of eighteenth cervical
vertebra, 2¾ inches; height of centrum, same vertebra, 2 inches; length of centrum of
twenty-fifth cervical vertebra, 3 5/8 inches.
S. W. WILLISTON.

University of Kansas, Oct. 25.

290
SCIENCE.
[VOL. XVI. No. 407

......

Structure of the Plesiosaurian Skull.

IN his recently published "Manual of
Paleontology" (p. 1067) Lydekker makes the statement, in his definition of the
Lynapto- saurian branch, that there are "no ossifications in the sclerotic of the
eye," and repeats it in his yet more recent "Catalogue of Fossil Reptilia."
Upon this authority, I stated in my recent letter to Science that sclerotic plate's had
not been previously described for this branch, including the Chelonia and Sauropterygia.
This is not correct, as Dr: Baur kindly informs me. He says, "Sclerotic plates are
present in the Testudinata, as mentioned by Huxley and Hoffmann. I have found them in
Pleurodira, Cryptodira, and Trionycha."

I do not wish to say that this character, and certain other
ones, such as the co-ossification of the jaws, absence of parietal foramen, etc. , are of
high classificatory value, but rather that their discovery will require a revision of
definitions hitherto given.

S. W. WILLISTON.Lawrence, Kan., Nov. 12.

References:

Nicholson, H. A., and Richard Lydekker. 1889. A manual of palaeontology for the
use of students, with a general introduction on the principles of palaeontology. 3d
ed., London, vol. II xi + 889-1624, figs. 813-1354. 1st and 2nd eds.

Lydekker, Richard 1890. Catalogue of the fossil Reptilia and Amphibia in the
British Museum. Part IV. Containing the orders Anomodontia, Ecaudata, Caudata, and
Labyrinthodontia; and supplement. London. xxiii + 295 pp., 66 figs.